A second man has been arrested by detectives investigating the murder of a respected historian found knifed to death at his home.

The suspect, a 50-year-old from Peterborough, is being held on suspicion of murdering Oxford-educated Adrian Greenwood, 42, who was found dead by his cleaner.

His body was discovered in the hallway of his four-storey property in Iffley Road, Oxford, at around 3pm last Thursday, Thames Valley Police said.

A 26-year-old man who was arrested on suspicion of murder on the day Mr Greenwood’s body was found was released without charge on Saturday.

Detective Chief Inspector Kev Brown, of Thames Valley Police’s major crime unit, said it was crucial anyone with information about Mr Greenwood’s background or murder came forward.

He said: “The investigation team would like to hear from anyone who has details about Mr Greenwood’s associates, or anyone who has had a personal or business engagement with him in the last few weeks.”

Police re-released a CCTV image of Mr Greenwood captured at a Sainsbury’s store in Kidlington two days before his death in a bid to jog memories.

Mr Greenwood - a collector of Harry Potter books - was the victim of a “vicious and sustained” attack. A post-mortem examination found he died from multiple stab wounds.

He went to £35,000-a-year Tonbridge School in Kent, where he was taught by Sir Anthony Seldon, the historian and biographer of John Major, Tony Blair and Gordon Brown.

A graduate of politics, philosophy and economics from Christchurch College, Oxford, he followed in his former history teacher’s footsteps by becoming an historian and biographer.

He penned two historical biographies and also traded rare and antiquarian books, including texts which he provided to the British Library and Getty Museum, according to his website.

Mr Greenwood gained national media attention in 2010 when one of his first edition Harry Potter books, worth £6,000, was stolen from an exhibition gallery in Woodstock, Oxfordshire.

Mr Brown added: “I would like to reassure the public that we are conducting a thorough investigation into this vicious murder. We have had specialist search teams at the scene, including a police dog.